Infection patterns of dengue, Zika and endosymbiont Wolbachia in the mosquito Aedes albopictus in Hong Kong

Detection of a sympatric cryptic species mimicking Aedes albopictus (Diptera: Culicidae) in dengue and Chikungunya endemic forest villages of Tripura, India, posing a daunting challenge for vector research

The Aedes (Stegomyia) albopictus (Skuse, 1985) (Diptera: Culicidae) is one of the major vectors for Dengue and Chikungunya. However, our study uncovered another mosquito species morphologically similar to Ae. albopictus but is genetically different. The male genitalia of this species possess minute differences in the IX tergum with Ae. albopictus. Nucleotide diversity and mean genetic distance analysis confirmed the genetic difference from Ae. albopictus and other Aedes species. However, this species has a significant degree of genetic similarity with the cryptic species of Ae. albopictus earlier reported from Vietnam and China. The time tree revealed the median divergence time of this species and Ae. albopictus species to be approximately 36.13 million years ago. This study marks the discovery of an Aedes nr. Albopictus species resembling Ae. albopictus in India and third in the world, also reports the distinct morphological feature of the male genitalia for the first time. Our study indicates the sympatric behavior of this species as it shares the breeding habitat of Ae. albopictus. The absence of endosymbiont Wolbachia in this species raises the possibility of reproductive isolation with Ae. albopictus leading to sympatric speciation and increasing virus-carrying capability for this species, having significant implications for vector-borne disease control.

Synthetic rational design of live-attenuated Zika viruses based on a computational model

Many viruses of the Flaviviridae family, including the Zika virus (ZIKV), are human pathogens of significant public health concerns. Despite extensive research, there are currently no approved vaccines available for ZIKV and specifically no live-attenuated Zika vaccine. In this current study, we suggest a novel computational algorithm for generating live-attenuated vaccines via the introduction of silent mutation into regions that undergo selection for strong or weak local RNA folding or into regions that exhibit medium levels of sequence conservation. By implementing our approach to the ZIKV genome, we demonstrated strong correlation between the degree of conserved RNA local energy disruption and replicative ability of the viruses in Vero cells. In vivo analysis in the AG129 mouse model demonstrated the ability of the attenuated ZIKV strains to stimulate protective immune response against the wild-type virus. In some cases, up to 80% of the AG129 mice survived both the vaccination and the challenge with the wild-type strains, while 0% of the nonvaccinated mice survived the challenge. Our study provides a blueprint for a computational design of live-attenuated vaccine strains that still preserve immunogenic epitopes of the original RNA viruses. We believe that the approach is generic and can be used successfully for additional viruses.

Global genomics of Aedes aegypti unveils widespread and novel infectious viruses capable of triggering a small RNA response

The mosquito Aedes aegypti is a prominent vector for arboviruses, but the breadth of mosquito viruses that infects this specie is not fully understood. In the broadest global survey to date of over 200 Ae. aegypti small RNA samples, we detected viral small interfering RNAs (siRNAs) and Piwi interacting RNAs (piRNAs) arising from mosquito viruses. We confirmed that most academic laboratory colonies of Ae. aegypti lack persisting viruses, yet two commercial strains were infected by a novel tombus-like virus. Ae. aegypti from North to South American locations were also teeming with multiple insect viruses, with Anphevirus and a bunyavirus displaying geographical boundaries from the viral small RNA patterns. Asian Ae. aegypti small RNA patterns indicate infections by similar mosquito viruses from the Americas and reveal the first wild example of dengue virus infection generating viral small RNAs. African Ae. aegypti also contained various viral small RNAs including novel viruses only found in these African substrains. Intriguingly, viral long RNA patterns can differ from small RNA patterns, indicative of viral transcripts evading the mosquitoes' RNA interference (RNAi) machinery. To determine whether the viruses we discovered via small RNA sequencing were replicating and transmissible, we infected C6/36 and Aag2 cells with Ae. aegypti homogenates. Through blind passaging, we generated cell lines stably infected by these mosquito viruses which then generated abundant viral siRNAs and piRNAs that resemble the native mosquito viral small RNA patterns. This mosquito small RNA genomics approach augments surveillance approaches for emerging infectious diseases.

The interplay between vector microbial community and pathogen transmission on the invasive Asian tiger mosquito, Aedes albopictus: current knowledge and future directions

The invasive Asian tiger mosquito Aedes albopictus is nowadays broadly distributed with established populations in all continents except Antarctica. In the invaded areas, this species represents an important nuisance for humans and, more relevant, it is involved in the local transmission of pathogens relevant under a public health perspective. Aedes albopictus is a competent vector of parasites such as Dirofilaria and viruses including dengue virus, Zika virus, and chikungunya virus, among others. The mosquito microbiota has been identified as one of the major drivers of vector competence, acting upon relevant vector functions as development or immunity. Here, we review the available literature on the interaction between Ae. albopictus microbiota and pathogen transmission and identify the knowledge gaps on the topic. Most studies are strictly focused on the interplay between pathogens and Wolbachia endosymbiont while studies screening whole microbiota are still scarce but increasing in recent years, supported on Next-generation sequencing tools. Most experimental trials use lab-reared mosquitoes or cell lines, exploring the molecular mechanisms of the microbiota-pathogen interaction. Yet, correlational studies on wild populations are underrepresented. Consequently, we still lack sufficient evidence to reveal whether the microbiota of introduced populations of Ae. albopictus differ from those of native populations, or how microbiota is shaped by different environmental and anthropic factors, but especially, how these changes affect the ability of Ae. albopictus to transmit pathogens and favor the occurrence of outbreaks in the colonized areas. Finally, we propose future research directions on this research topic.

Prevalence and molecular characterization of Wolbachia in field-collected Aedes albopictus, Anopheles sinensis, Armigeres subalbatus, Culex pipiens and Cx. tritaeniorhynchus in China

Wolbachia are maternally transmitted intracellular bacteria that can naturally and artificially infect arthropods and nematodes. Recently, they were applied to control the spread of mosquito-borne pathogens by causing cytoplasmic incompatibility (CI) between germ cells of females and males. The ability of Wolbachia to induce CI is based on the prevalence and polymorphism of Wolbachia in natural populations of mosquitoes. In this study, we screened the natural infection level and diversity of Wolbachia in field-collected mosquitoes from 25 provinces of China based on partial sequence of Wolbachia surface protein (wsp) gene and multilocus sequence typing (MLST). Among the samples, 2489 mosquitoes were captured from 24 provinces between July and September, 2014 and the remaining 1025 mosquitoes were collected month-by-month in Yangzhou, Jiangsu province between September 2013 and August 2014. Our results showed that the presence of Wolbachia was observed in mosquitoes of Aedes albopictus (97.1%, 331/341), Armigeres subalbatus (95.8%, 481/502), Culex pipiens (87.0%, 1525/1752), Cx. tritaeniorhynchus (17.1%, 14/82), but not Anopheles sinensis (n = 88). Phylogenetic analysis indicated that high polymorphism of wsp and MLST loci was observed in Ae. albopictus mosquitoes, while no or low polymorphisms were in Ar. subalbatus and Cx. pipiens mosquitoes. A total of 12 unique mutations of deduced amino acid were identified in the wsp sequences obtained in this study, including four mutations in Wolbachia supergroup A and eight mutations in supergroup B. This study revealed the prevalence and polymorphism of Wolbachia in mosquitoes in large-scale regions of China and will provide some useful information when performing Wolbachia-based mosquito biocontrol strategies in China.

The mosquitoes Aedes albopictus, Anopheles sinensis, Armigeres subalbatus, Culex pipiens and Cx. tritaeniorhynchus are native to China and the major vectors in the transmission of arboviruses, protozoans and nematodes. Recently, an innovative biocontrol strategy has been developed and evaluated based on the ability of Wolbachia to induce cytoplasmic incompatibility (CI), as well as interfere with the infection and replication of pathogens. Since the ability to induce CI largely depends on the density and diversity of Wolbachia, we investigated and characterized the natural infection of Wolbachia in above-mentioned five species of field-collected mosquitoes in 25 provinces of China. The results showed that the positive rates of Wolbachia infection were high in mosquitoes of Ae. albopictus, Ar. subalbatus and Cx. pipiens in large-scale regions of China and low in Cx. tritaeniorhynchus in Guizhou province. Phylogenetic analysis based on Wolbachia surface protein (wsp) gene and five multilocus sequence typing (MLST) loci indicated the high polymorphism of Wolbachia in Ae. albopictus, and low polymorphisms in Ar. subalbatus and Cx. pipiens. This finding contributes to the understanding of the nationwide distribution of Wolbachia and the potential application of this biocontrol strategy in China.